1. Determining the Relative and Absolute Age of Map Units
GEOL 3000 Geologic Maps
Determining the Relative and Absolute Age of Map Units

2. Relative Age Dating - Superposition

3. Up isn’t always Younging

4. Up Indicators Graded Bedding Pillowed Lavas
Amygdaloidal Zones in Lavas
Cross-bedding
Ripple Marks

5. Sedimentary Facies – Time Trangressive Units

6. Paleogeography of Middle Laurentia in the Paleozoic

8. Advanced Transgression
Regression

9. Paleozoic Formations of the Upper Midwest

10. Principles of Faunal Succession and Faunal Assemblage
Index Fossils
- Widespread distribution
- Restricted, known time of existence
- Common to many environments

11. The Jordan Sandstone
Unconformity
Missing Fossils

12. Gaps in the Geological Record Unconformities
Siccar Point, Scotland
“The mind seemed to grow giddy looking so far into the abyss of time”
John Playfair – Illustrations of Huttonian Theory (1809)

13. Creating Unconformities
Nonconformity
Angular Unconformity
Grand Canyon
Stratigraphy
Disconformity

14. Unconformities or
Pinch-outs?

15. Gaps in the Minnesota Timescale

16. Regional Correlation of Units Piecing the Rock Record Together

17. Relative Time for Intrusive Igneous Rocks Principle of Cross-cutting Relationships

18. Global Time Markers Volcanic Ash Eruptions

19. Global Time Markers Meteor Impacts
K-T Boundary
mudstone-impact layer
coal
K-T impact site

20. The First Major Extinction Event ??
The Ga Sudbury Impact
The First Major Extinction Event ??

21. Global Time Markers Magnetic Reversals

22. Global Time Markers Climate Change

23. Absolute Age Determinations Radiometric Dating

24. Radioactive Isotopes

25. Radioactive Decay

26. Radioactive Decay Half-life
Zircon
ZrSiO4
U substitutes for Zr, but Pb does not.

27. Rb-Sr Dating of a Granite
87Rb  87Sr; 86Sr is stable
Rb – chemically substitutes for K
Sr – chemically substitutes for Ca
Isochron
t=2
t=1
87Sr/86Sr
Metamorphism
at t=1
87Sr/86Sr°(m)
t=0
87Sr/86Sr°
87Rb/86Sr
Ca-plagioclase
Granite whole rock
K-feldspar
Biotite (K-rich)